In recent years semiconductor memories, such as radio frequency (RF) tags (which may be referred to as radio frequency identifiers (RFIDs)), having a radio communication function have increased in number. RF tags which perform radio communication in an ultra-high frequency (UHF) band are being standardized by EPCglobal (registered trademark) and are used for commodity tags and the like. Furthermore, RF tags to which an image display device, such as electronic paper, is connected and RF tags to which a sensor is connected are also known.
An RF tag performs radio communication with a reader-writer. If the RF tag receives data for performing each application, then the RF returns to the reader-writer a response signal to the effect that it received the data. If the reader-writer receives the response signal, then the reader-writer transmits the next data. If the reader-writer does not receive the response signal in a determined period, then the reader-writer determines that a communication error has occurred, and transmits the same data again. Reply strength tends to weaken especially with a passive type RF tag which is not equipped with a battery and which operates on the basis of power supplied from a reader-writer. As a result, a communication error tends to occur.
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However, though application processing based on data received the last time is normally performed in a semiconductor memory having a radio communication function, the same data may be received again. In that case, the same processing is repeated and abnormal operation may occur.
With an RF tag which receives image data from a reader-writer and which causes a display device to display the image data, for example, the following problem may arise if the same image data are processed more than one time. For example, the length of a displayed image may increase. Furthermore, with an RF tag which receives a sensor value acquisition command from a reader-writer, there is a case where the last command is normally processed and where the command is processed again. In that case, a plurality of values may be stored in a memory as a sensor value at a given time.